A few years ago I forced the chef John Torode to taste-test 80 supermarket-available organic products with me. I still wake sometimes in the middle of the night shaking in terror at the memory of that day, which has since infested my nightmares. A startling number of the items we tried - the cheeses and the sausages, the marmalades, pasta sauces and smoked salmon - were, and I've chosen these words carefully, complete dreck. I recall standing in Torode's kitchen shouting: 'Bring on the chemicals! Please! Somebody adulterate this food!'

A clear point was made that day. Where food is concerned, principle is not enough; an ethical approach may be a lovely thing we can all embrace, but if the result doesn't eat well it's a waste, not just of time but of resources. Restaurant kitchens carry a further burden. They might claim a sourcing policy as virtuous as a nunnery on Good Friday, but if they don't know how to cook, all the work out in the fields will have been wasted. Some may regard this as blasphemy, but I think there is greater virtue in a factory broiler cooked by somebody who knows what they are doing than a poulet de Bresse massacred by an incompetent mouthing platitudes. At least the broiler wasn't slaughtered in vain.

But the ideal situation is, of course, the good stuff cooked well, which is what Cristina Anghelescu does at her delightful little restaurant Rosemary Lane, a few hundred yards to the east of the Tower of London. It's a pretty name for a place located on an ugly street: Rosemary Lane, a converted pub, looks out over the perfect spot for a carjacking. No matter. Inside, there are handsomely varnished, wood-panelled walls hung with vivid photographic art and a menu fat with promise. Some of it reads a little fussily. If it's on the plate it's also on the menu. But when the food arrives it makes sense and mostly, I think, because of an uncommon interest in vegetables. The classic French approach is to start with a lump of protein - the slab of dead cow, the shiny-eyed fishy - and build everything up from there. Here, animal and vegetable get equal billing.

A lot of those vegetables come via the fabulous Booths at Borough Market, and many of those are organic. 'If he can't find the right thing for me he won't let me have it,' Anghelescu told me after dinner. The rest - leaves, baby vegetables - come from Secretts, the remarkable farm which won our Observer Food Monthly Producer Award this year. The clearest sign of intention was in the 'amuse': a curl of perfectly roasted red pepper, a slice of Italian yellow tomato, a chunk of sweet and sour dark-roasted onion. You know how much I like my dinner to have had a pulse, but the fresh vibrant flavours of this had me. I was not at all surprised to learn later that the chef spent part of her training at Chez Panisse in California, which made its name with this sort of ingredient-worship.

It was there again in the starters: what was described as a wild mushroom flan (but was more a light, fluffy mousse) arrived with heaps of green herbs and long silky fronds of enoki mushroom. A pate of organic chicken livers, intense and rich, came with a tremendous celeriac remoulade, though it may have been the remoulade that came with the pate. It really was a model of its kind: crisp, with a clever balance between celeriac and the lightly-acidic dressing. Mains are solid and fulsome rather than prissy; perhaps in the case of my lamb dish a little too fulsome. Tottering on my plate was a whole rack of Lancashire lamb - eight chops - which came with a dense ratatouille of heirloom peppers, spring onions and cherry tomatoes. I was not surprised when Anghelescu told me that the lamb cost almost as much as the price of the £17 dish, and that she could serve it because other things - her Italian yellow tomato and grilled pepper soup, or her herb risotto - subsidised them. She could easily have served half that amount of lamb. Still, it was very good meat.

We liked a big, fat, crisp-skinned breast of poulet de Bresse and the fresh baby carrots, fennel and leeks in a creamy onion veloute which came with them. We liked the onion and the walnut bread and the cheesy unsalted butter to go with it. The only technical faults lay in the puddings, and they were minor. Both a vanilla panna cotta and a mandarin orange cheesecake were a little overset, but I suspect I'm only mentioning this to reinforce my hard-man of food credentials.

A heavy hand with the gelatine aside, I like Rosemary Lane. There is nothing doctrinaire about it (Anghelescu told me that she won't use organic if the product is not good enough). There is no attempt to make food follow principle. Instead, the two ride hand in hand. Anghelescu could not cook her food unless she obtained those ingredients. And getting ingredients of that quality demands certain principles. It is, I think, the ultimate virtuous circle.